I cannot speak for OCS, but at USNA, commissioned lineal number is based on class rank. While I 100% agree that you will not directly be selected/non-selected for LCDR based on your time or performance at OCS/USNA/ROTC, the second order effect of your resultant lineal number there can impact selection (though that might not be the case for OCS, depending on the performance/TIS/Alphabetical debate... you might just be better off if your last name starts with A vice Q).
For instance, this last year, the IZ/BZ cut off for the IW LCDR board was folks with a JUN05 LT promotion date. Two Officers from the same commissioning source, commissioned the same date, found themselves split between the IZ and BZ grouping. There is a set quota size for the zone that is blind to lineal/commissioning source/etc. In this case, the class standing did matter. Not necessarily as far as what is briefed to the board, but whether that Officers record went before the board as an IZ or BZ record. I would argue there is a more likely selection opportunity for the former vice the later. Further, the day I was commissioned, we had 6 IW Officers come from USNA as well as some from OCS. Though all commissioned the same day, the OCS folks had a lower lineal number than the USNA folks...
If that was confusing, I?d be happy to try to explain further, just PM me. BTW, this all sounds like something Malcolm Gladwell would discuss in Outliers...